Encapsulated electrical coil and method of making



United States Patent 3,383,363 ENCAPSULATED ELECTRICAL COIL AND METHOD 0F MAKING Robert R. Novick, Fort Wayne, InrL, assignor to Square D Company, Park Ridge, 1., a corporation of Michigan Filed Feb. 8, 1966, Ser. No. 525,943 3 Claims. (Cl. 336-96) ABSTRACT OF THE DISCLOSURE An insulative cord helically wound about the wall of an annular coil body holds a terminal plate and serves to space the coil body from a mold during encapsulation.

This invention relates to an encapsulated electrical coil having improved means for providing predetermined and uniform .spacing between the body of the coil and the walls of a mold during encapsulation of the coil body to form the completed coil, and to a method of making the completed coil.

One of the problems encountered in the manufacture of encapsulated electrical coils is the difficulty of providing uniform spacing between the surface areas of the coil body and the walls of the mold during encapsulation thereby to insure that the encapsulating material is of the proper thickness throughout. This problem is solved, in accordance with the present invention, by means of an insulative cord wound helically several times about the coil body prior to encapsulation. The several convolutions of the cord serve as a spacing means between the coil body and the mold during encapsulation. The cord also reinforces the encapsulating material and, in the preferred embodiment, also holds a treminal board for the the coil in position.

An object of this invention is to provide an improved encapsulated electrical coil having an insulative cord wound several times about the coil body, the cord serving as a spacer during encapsulation of the coil body.

Another object is to provide an improved encapsulated electrical coil having a terminal board secured to the coil body by an insulative cord wound about the terminal board and coil body and serving also as a spacing means between the coil body and thewalls of a mold during encapsulation of the coil.

A further object is to provide an improved method of manufacture of an encapsulated electrical coil.

Further objects and advantages of this invention will become apparent from the following specification wherein reference is made to the drawings, in which:

FIG. 1 is a perspective view of a coil body and terminal board of an electrical coil in accordance with this invention, a cord being wound about the terminal board and the coil body preparatory to encapsulation;

FIG. 2 is a sectional view taken generally as indicated at 22 in FIGURE 1 and showing the coil body Within a mold prior to encapsulation;

FIG. 3 is a sectional view similar to FIGURE 2 but after encapsulation and with the mold shown in phantom; and

FIG. 4 is a perspective view of a completed coil.

Referring to FIGURE 1, there is shown an annular coil body 10 preferably of generally rectangular configuration and comprising a plurality of layers of closelyspaced turns of a continuous strand of insulated wire 11. The coil body 10 is preferably formed by winding the wire 11 upon a removable bobbin (not shown) defining and received within a central opening 12. Opposite terminal portions 13 and 14 of the wire 11 extend from 3,388,363 Patented June 11, 1968 "Ice the coil body 10 and, in the illustrated embodiment, are electrically connected to a composite terminal board 15.

The terminal board 15 comprises an elongated rigid insulating strip 16 having a pair of perforated metal terminal plates 19 and 20 secured to its opposite end portions, respectively, as by an adhesive or rivets not shown). The terminal portions 13 and 14 are electrically connected to the terminal plates 19 and 20, respectively, as by soldered joints 21 and 22. In accordance with this invention, an insulative cord 24 formed of vegetable fiber or synthetic material is wound about the coil body helically as indicated, the convolutions of the cord 24 passing through the central opening 12 and some passing over the insulating strip 16 to the hold the terminal board 15 in assembled position on the coil body 10. The cord 24 may be knotted where necessary as at 25 if vegetable fiber is used, or the necessary junctions of the cord may be heat sealed if a plastic cord having the proper thermal characteristics is used. The cord 24, if of vegetable fiber, may be impregnated with a suitable insulating varnish or the like to improve its dielectric properties. Although the cord 24 preferably is continuous, as shown, it is apparent that more than one length of cord may be used as desired.

In order to encapsulate the assembled coil body 10 and terminal board 15 of FIGURE 1 with a coating of insulating material, the assembly is placed in a two-part mold 28 as shown in FIGURES 2 and 3. Although only one part of the mold 28 is shown, it will be understood that the two parts of the mold are identical, each having a central projection 29 which enters the opening 12 in the coil body 10 and defines an annular chamber 30 for receiving one-half of the coil body 10. Preferably, notches 31 formed in the mold receive respective opposite end portions of the terminal plates 19 and 20. The outer surfaces of the coil body 10 are spaced from the bottom and side walls of the mold by the convolutions of the cord 24 and the surfaces of the coil body 10 defining the central copening 12 are spaced from the side walls of the projecting portions 29 of the mold 28 by the portions of the convolution of the cord 24 passing through the central opening 12.

After the assembled coil body and terminal board are placed in the mold 28, a suitable encapsulating material 32 in liquid form and compatible with the insulation on the wire 11 and with the cord 24 is introduced into the chamber 30 as by being poured through an orifice 33 at the top of the mold 28. The encapsulating material 32 fiow between the outer peripheral surfaces of the coil body 10 and the outer walls of the mold as well as between the surfaces defining the opening 12 and the side walls of the projections 29 because of the clearance spaces provided by the cord 24. It is to be noted that because the cord 24 is helically wound about the coil body 10, passages are provided for the liquid 32 to fiow into and fill all spaces between the coil body 10 and the walls of the mold 28. The material 32 may be thermosetting or it may be of the type that hardens at room temperature, with or without the addition of a hardener, such as an epoxy compound.

After the material 32 has solidified, the mold 28 is remove-d and the finished coil as shown in FIGURE 4 has a solid coating of insulating material 32 of substantially uniform thickness covering the entire coil body 10, except for the upper surface above the terminal board 15. In the illustrated embodiment, the coil body 10 and the mold 28 are so proportioned that a thicker layer of the material 32 may be provided above the terminal board 15 by completely filling the mold 28 during the pouring operation. It will be understood that if the terminal board 15 is not used, the mold could be proportioned so that the coating 32 would be of uniform thickness throughout.

Although, for illustrative purposes, a simple pouring operation has been described for filling the mold 28 with an encapsulating material 32, it will be understood that other well-known methods for introducing encapsulation material into mold may be used without departing from the scope of the invention.

I claim:

1. A method of making an encapsulated electrical coil which com-prises winding a strand of insulated wire into a multi-turn annular coil body having an outer periphery and a central opening, electrically connecting the ends of the strand of wire to a terminal board after the coil is wound and positioning the terminal board against a portion of the outer periphery of the coil body, winding an insulative cord helically about the coil body with the convolutions of the cord passing through the central opening and at least one of the convolutions of the cord passing over the terminal board to thereby hold the terminal board in its position on the periphery of the coil body, placing the coil body with the terminal board and cord wound thereon in a mold with the cord defining a space between the coil body and at least some of the walls of the mold, introducing encapsulating material into the mold to the extent necessary to fill the space between the coil body and the walls of the mold, allowing the encapsulating material to solidfy, and removing the encapsulated coil from the mold.

2. An encapsulated electrical coil comprising: an annular coil body formed of a plurality of turns of an insulated electrical conductor and having an outer periphery and a central opening, a terminal board electrically connected to a pair of ends of the electrical conductor, an insulative cord forming a plurality of spaced convolutions about the periphery of the coil body and and passing through the central opening with at least one of the convolutions positioning the terminal board on the outer periphery of the coil body, and a layer of insulating material encapsulating the coil body, the terminal board and the cord to provide a completed coil, said layer of insulating material providing an outer surface for the completed coil and having a thickness substantially equal to the diameter of the cord throughout most of the surface area of the completed coil.

3. A coil in accordance with claim 1 characterized in that the cord is formed of flexible synthetic material.

References Cited UNITED STATES PATENTS 497,535 1893 Cummings. 2,131,987 10/1938 Studt et al. 336-96 2,243,553 5/1941 DEntremont 336-192 2,275,967 2/ 1943 Keillor et -al. 336209 3,243,752 3/1966 Lawrence 336-96 FOREIGN PATENTS 1,047,545 12/ 1956 Germany.

191,550 1923 Great Britain.

227,288 1925 Great Britain.

DARRELL L. CLAY, Primary Examiner.

LEWIS H. MYERS, LARAMIE E. ASKIN,

Examiners. T. J. KOZMA, Assistant Examiner. 

